In 1943 a redesigned KV-1 was fitted with a 85mm gun. This design was called IS-1 or IS-85. The letters IS stood for Iosef Stalin and was a sucsessful heavy tank model. It had a modified hull, improved suspension and transmission. It was heavily armoured and had a new turret. Later versions of IS-1 were fitted with 100 mm or 122 mm guns and earlier units were rearmed to be able to smash the front of a German Panther V and Tiger VI. By this model the power was evened between the two armor cobatants and this state continued to the end of the war a couple of years later.